The invention relates to an injection molding machine with a frame which is C-shaped viewed from the side, the legs of which are pushed apart at their free ends by the effect of the locking force, wherein the two die platens associated with the legs are kept parallel in that pivoting occurs between at least one die platen and the associated leg.
Normally (EP 0 311 133 B2) such injection molding machines with beamless mold locking means allow the pivoting of the stationary die platen together with the associated leg of the frame taking up the locking force, wherein a joint between the moveable die platen and the other leg of the frame makes it possible that when the locking force is applied, the moveable die platen is set parallel to the stationary die platen. It is also possible to uncouple the two die platens from the associated legs of the tension frame by means of joints (see DE 295 16 388 U). In both cases, the joints which provide the pivoting can be formed by a bearing with parts which pivot opposite one another (for example rotatable axle pins) or by means of a deformable retaining part, possibly integrated into the machine frame.
In particular with the standard injection molding machines provided with beams, it has long been known to monitor the running of the process, in that the locking force actually applied to the tool is registered by measuring the hydraulic pressure or by measuring the strain on the beam within the locking and opening cycle. Monitoring of the strain on an individual beam is sufficient to protect the mold against pieces mistakenly being left inside the mold and for determining excessive pressure inside the mold, which distends the mold. It is also possible in principle, by simultaneous monitoring of the strain on all four beams, to determine asymmetrical positioning of the edges of the mold or a loading on one side of the mold because of the mold being arranged asymmetrically or not being filled evenly. However, such a determination requires a continuous comparison of differences in the strain on the individual beams occurring for other reasons, so the monitoring of all the beams to determine disturbances in the symmetry of the apparatus or the course of the process has not been achieved.